1 Field of the Invention
The present invention relates to the measurement of sub-surface ocean temperature profiles and more particularly to an improved method of and apparatus for remotely measuring such temperature profiles from an aircraft or the like.
2. Description of the Prior Art
Profiles of ocean water temperature as a function of depth are important basic scientific data used by the oceanographic community for several purposes including determination of the effect on climate. A technique employed in the past for measuring such profiles involves the use of many temperature sensing elements spaced on a cable and towed by a ship. This is costly, time consuming and generally unsuited to high spatial and temporal resolution coverage of large ocean areas. Furthermore, the technique cannot be used for mapping ocean temperature profiles, that is, temperatures over wide areas of water, because the measuring time is too long compared to the time over which sea temperatures vary.
Another technique is described in Patent No. 4,123,160 in which a laser beam is used to illuminate the water and observation is made of the Raman scatter from the monomer and hydrogen bonded polymeric forms of water, the ratio of which is a function of temperature. This technique is vulnerable to interference from high background illumination, such as sunlight, because of the relatively wide optical bandwidth of the Raman scattering. Furthermore, in this technique there is differential absorption over the Raman band as light transits the water column. Depolarization effects of the water column also limit the effectiveness of the technique when polarization spectroscopy is employed.
Still another laser remote sensing method has been used in limited experiments, see "SPEED OF SOUND AND TEMPERATURE IN THE OCEAN BY BRILLOUIN SCATTERING" by Hirschberg, et al., Applied Optics, Aug. 1984, pages 2624-2628, inclusive. This method relies on the wavelength shift associated with Brillouin scattering from the water. This shift, however, is small so that extremely high resolution is required in optical measurement of the wavelength shift. Typically a Fabry-Perot interferometer is used to resolve the Brillouin shift. However, an interferometer requires a well collimated light source which generally is incompatible with remote sensing applications, that is, because of spreading, light must be collected from a much larger field of view than is possible with an interferometer.
This invention is directed to the measurement of sub-surface ocean temperatures while avoiding these disadvantages.